1. Field of the Invention
The present invention relates generally to optical navigation, and more particularly, to an optical navigation sensor which includes an integrated charge pump for providing a supply voltage to a light source and a method of providing the supply voltage to the light source.
2. Description of the Prior Art
In a conventional optical navigation system, at least two direct current-to-direct current (DC-DC) boost converters are required to provide electrical power to internal components of the optical navigation system, one of which provides a supply voltage to an optical navigation sensor of the optical navigation system, and the other of which provides another higher supply voltage to a light source of the optical navigation system.
Please refer to FIG. 1, which schematically illustrates a conventional optical navigation system 10. External DC-DC boost converters 110 and 120 coverts power supplied by a battery 160 to generate supply voltages VDD1 and VDD2, to a driving circuit 130 of an optical navigation sensor 100 and a light source 140, respectively. In addition, to detect whether a fault event that a terminal of the light source 140 is improperly shorted to the ground occurs, a sensing circuit 150 is required. Such fault event may cause a large current to flow through the light source 140, thereby making the light source 140 to generate too strong light that may be harmful to user's eye. When the sensing circuit 150 detects the fault event, the sensing circuit 150 informs the driving circuit 130. The driving circuit 130 accordingly issues a control signal LSR_NEN to turn off a switch SW1 connected between the light source 140 and the supply voltage VDD2. When the path between the supply voltage VDD2 and the light source 140 is cut off, the light source 140 is unable to emit the light, thereby assuring the safety of user's eye.
However, there are two problems in such design. First, the external DC-DC boost converter 120 consumes considerably large power because the DC-DC booster converter 120 stays active all the time. Second, a control pin for transmitting the control signal LSR_NEN to turn off the switch SW1 is necessary. However, this increases the pin count of optical navigation sensor 100 and leads to the increasing of the hardware cost. Additionally, the requirement of switch SW1 also leads to the increasing of the hardware cost.